What are Petoskey stones?
Even though they’re found in the Great Lakes, Petoskey stones are actually fossilized coral. You can tell a Petoskey stone by its honeycomb pattern (in fact, the word “hexagon” is part of the scientific name). Those are the corallites, the skeletons of once-living coral polyps. The dark center of each polyp was the mouth, and the lines radiating out from it were actually tiny tentacles. Because the coral couldn’t move, it had to use these tentacles to grab algae, plankton and other food that happened to come along.
Where do they come from?
The now-extinct Petoskey stone coral known as Hexagonaria percarinatum existed during the Devonian period, which was about 419 million to 359 million years ago. These incredible fossils date back to the middle of that period, about 416 million to 396 million years ago. Devonian-era rocks form a large amount of Northern Michigan’s bedrock.
Maybe that’s why Michigan Rock Hunting is the Best on Earth
At the time, Michigan was in a very different spot on the globe. Much closer to the equator, the Great Lakes were once one shallow tropical sea. A Devonian period coral reef would have had clams, sponges, squids and fish, but also a lot of creatures unfamiliar to us today. Scientists think Hexagonaria coral lived and looked a lot like modern-day coral.
You’ll probably recognize a few names here. Fossilized Hexagonaria is only found in the rock layer known as Alpena Limestone, which is part of the Traverse Group of rocks from the Devonian period. These rocks were mainly concentrated in what’s now Little Traverse Bay. There are actually seven types of Hexagonaria coral that became Petoskey stones, but you’d probably have to be an expert to spot the difference from one Petoskey stone to the next.
Now fast-forward millions of years.
Technic shifts moved Michigan north and pushed the peninsulas up out of the water. Michigan’s climate could no longer support tropical sea life. Organisms that couldn’t migrate or adapt, like Hexagonaria, died out and under certain conditions became fossilized.
During the last ice age, about 10,000 years ago, the glaciers that carved out the Great Lakes and filled them with fresh water scooped these fossils out of the bedrock and deposited them on the lakeshore. Most Petoskey stones we find today have been smoothed out by erosion from water and sand, but it’s still possible to find rough Hexagonaria fossils in some Northern Michigan rock quarries.
Where does the name “Petoskey” come from?
The legend of the name “Petoskey” dates back to the 1700s. The story goes that a Frenchman with noble blood visited Northern Michigan, became a fur trader, and married an Ottawa Indian princess. The Frenchman was given the name Neatooshing and eventually became the tribe’s chief.
Neatooshing’s first son was born while he and his family were camping on the Kalamazoo River. Legend says he looked at the sunshine on his son’s face and said “His name shall be Petosegay,” meaning “rising sun” or “rays of promise.” Neatooshing predicted a promising future for his son, and Petosegay grew into his name. He became a wealthy fur trader who eventually married the daughter of another great Ottawa chief, and helped establish the area we know today as Petoskey.
What’s the difference between Petoskey and Charlevoix stones?
Did you know not every piece of fossilized coral you find on the Great Lakes is a Petoskey stone? Some of them are actually Charlevoix stones. They come from another extinct type of coral, Favosites alpenensis. Both fossils originate from the Traverse Group of rocks, but Petoskey stones are mostly found near Petoskey, while Charlevoix stones are found (you guessed it) near Charlevoix.
Hexagonaria (Petoskey stone) coral has a large honeycomb shape, with a dark center and lines radiating out from it. Favosites (Charlevoix stone) coral has a much smaller honeycomb shape which is generally “hollow,” with no center dot or lines.
Did you know there are actually pink Petoskey stones?
These rarest of the rare Petoskey stones are known as “Pink Pets.” The pinkish-orange color comes from minerals like iron that leeched into the coral as it turned to stone. If you find one of these, you’re lucky indeed!
Where can you find Petoskey stones?
There are several great places to find Petoskey stones in Northern Michigan. Here are some of the top spots:
Charlevoix – Mt. McSauba, Lake Michigan Beach, Beaver Island, Fisherman’s Island State Park, North Point Nature Preserve
Petoskey – Petoskey State Park
Frankfort – Pt. Betsie Lighthouse
Leelanau County – Empire Beach, Leelanau State Park, Sleeping Bear Dunes National Lakeshore
Manistee – Orchard Beach State Par
If you have another good spot (that you’re willing to share), let us know!
Some tips for finding them
Look for rocky rather than sandy beaches.
Spring is the best time to go rock hunting, because lake ice and winter weather will push rocks to shore. Heading out in the rain or after a storm can help, too, but remember that stormy weather can also wash Petoskey stones off the beach into the water.
Here’s the good news: Looking in the water might be your best bet. Stones on the beach are more likely to be picked over by other rock hunters. You’ll find more rocks in the water, and the wetness helps make the distinct Petoskey stone pattern easier to spot. With each stone you find, it will only get easier to spot the next one.
It’s also important to know the rules around collecting stones. Here in Michigan, you’re only allowed to take home 25 pounds of stone each year. If you find a Petoskey stone weighing more than 25 pounds (first of all, congratulations), but the DNR has the right to confiscate it.